Atrial fibrillation (AF) is the most common chronic arrhythmia and affects an estimated 2.2 million people in the United States. This arrhythmia is associated with a significant degree of morbidity, accounting for approximately 75,000 strokes each year and is independently associated with a 1.5 to 1.9 fold risk of death. Despite the impact of AF, it is ironically one of the least well understood arrhythmias. The causative genes of lone AF are being studied extensively, but lone AF accounts for only 5% of all AF. The much more common acquired form of AF is likely due to a complex interaction between multiple environmental and genetic factors. To further identify these factors, one can begin by studying the contribution of family to the risk of acquired AF. Family case-control studies have been used extensively to more accurately quantify the familial aggregation of complex diseases. We hypothesize that presence of AF in first degree relatives is a risk factor for developing AF. In this study, we propose a family case-control study to help further quantify this risk. After correcting for established risk factors of AF, part of this risk will be accounted for by yet unidentified environmental risk factors associated within families. However, this will also provide a measure of the potential contribution of genetic risk and will highlight the need for further genomic studies of acquired AF. [unreadable] [unreadable] [unreadable]